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May 18, 2011 -- Chronic lower back pain doesn't just hurt. It also appears to cause thinning of certain regions of the brain, which may lead to cognitive impairments, a study shows.

Researchers studying the link between pain and such thinning had hoped that successfully treating back pain would halt that process. Instead, it reversed it. Six months after surgery or spinal injections, a brain region associated with pain -- the dorsolateral prefrontal cortex -- had thickened.

"We thought it would be able to slow down the thinning, but to actually recover was pretty amazing," says study researcher Laura S. Stone, PhD, a neuroscientist at McGill University in Montreal.

The study is published in The Journal of Neuroscience.

Brain Testing for Back Pain Patients

Stone and colleagues recruited 18 patients who were seeking treatment for chronic lower back pain, which they had had for at least a year. Prior to treatment, each patient had an MRI to measure cortical brain thickness and to assess brain activity during a simple cognitive test. Fourteen of those patients underwent similar testing half a year later. Their tests were compared to scans of 16 people without back pain.

"The extent of the thickening was surprising to us," says study co-researcher David A. Seminowicz, PhD, of the University of Maryland School of Dentistry. "Every patient who had less pain or decreased disability after treatment showed a thickening in that area."

That area is the dorsolateral prefrontal cortex, which plays an important role in how we perceive pain. While it was the only brain region that showed significant thickening after treatment, several other regions appeared to improve as well.

"There was a trend in a lot of different areas to get thicker," says Seminowicz, who is now planning studies to look at the long-term impact that treating back pain may have on the brain.

Link Between Pain and Brain Function

Pain also puts increased demands on the brain. Patients with lower back pain show an abnormal amount of brain activity when performing the same tasks as those who do not suffer from such discomfort. They often report difficulty concentrating, says Stone. In testing, they show impaired abilities in cognitive tasks and decision making, which may be related to the distracting influence of pain and the demands it puts on the brain.

Stone did not measure how well patients perform on such cognitive tests. But her study does show that patients who had undergone successful treatment for back pain had brain activation levels approaching those of healthy people.

While pain appears to be the cause of the thinning, it's not understood exactly how it happens, says Stone.

"Is it cells dying? Or do other things happen? Do the cells shrink? We don't know," she says. "But if we can figure out what causes the thinning and the thickening, we may be able to develop therapies that target that mechanism."